Rod mill loop control by imaging loop on differential detector system



1963 H. F. MISEROCCHI EI'AL 3,105,6 5

ROD MILL LOOP CONTROL BY IMAGING LOOP ON DIF'F'EREIH'IAL DETECTOR SYSTEM Filed Nov. 16, 1961 [7 FIG. 5

INVENTOR.

HENRY E MISEROCCHI BY PETER J. M CONNELL ATTORNEY tires This invention relates to the control of loops in a rapidly mov ng material which is self-luminous. More particularly the invention relates to materials which are selfluminous in the infrared although the invention is not limited thereto but includes materials which emit other optical radiations such as, for example, visible radiations.

Loop control is a serious problem in many plants Where self-luminous material in the form of bars, rods, tubes and the like is formed usually at considerable speed. The problem is most acute in steel rod and bar mills where the glowing rod may be moving at speeds up to almost 90 miles an hour. The invention, of course, is applicable to any self-luminous material in which a loop of predetermined dimensions needs to be formed. Throughout the remainder of this specification the invention will be described in conjunction with a steel rod or bar mill it being understood that the same instrumental organization may be employed with other self-luminous material such as rods or tubes of glass, hot drawn wire and the like.

In a steel rod or bar mill the original billet is passed through successive rolls being squeezed out into smaller and smaller size until it has reached the desired dimensions. This involves a great lengthening accompanied by an increase in speed of the material between pairs of rolls. Particularly near the finishing end, high speeds are encountered approaching 90 miles an hour in some installations. Under these conditions it is most essential that roll speed be controlled with a minimum of delay. If the rod were pulled taut between pairs of rolls nonuniform stretching will take place and a rod would be produced the diameter of which would not be uniform. Also in extreme cases the rod might break. Therefore, it is established practice to provide some reserve material in the form of a loop between the rollers so that the rod is not placed under tension. This loop must be sufiicient to provide the necessary slack but it must not be excessive otherwise the rod may cobble, throwing it out of the mill which can cause injury, damage to other equipment and at the very least requires an expensive shutdown and restarting.

It is customary in steel rod mills to observe the loop dimensions and to correct relative roll speeds when the loop assumes positions beyond a predetermined range. With fast moving bars this requires extremely rapid reflexes and at the least requires additional skilled manpower. There has, therefore, long been a need for reliable means of controlling loop dimensions quickly and preferably automatically. The solution of this problem constitutes the primary objective of the present invention.

Essentially the present invention produces an image of a portion of the rod as it races by and applies this image to a suitable ditferential detector system, for example one operating in the near infrared, giving an output signal which indicates departure of the rod from its predetermined normal position and which also corrects this departure. Correction may be effected by changing the speed of one or both pairs of rolls between which the loop is formed. As stated above the problem sounds simple. However, its solution has not been achieved though a need has long been felt. One of the reasons is that the instantaneous position of the rod for a normal loop must be Patented Get. 1, 15363 indicated very sharply and very positively. A second requirement which is vital in a steel mill is that the amount of correction to the speed of the rolls must decrease as the point of predetermined loop position is approached. If this condition is not met hunting will result which can produce excessive loads on the roll and servo drives and even set up a resonant whipping of the rod which causes it to oscillate beyond normal limits.

With steel mills where the temperature, size or ends sivity of the rod does not suddenly fluctuate within wide limits, simple instruments which satisfy the two requirements set forth above are capable of giving practically useful results. However, where large temperature, size or emissivity fluctuations are encountered, or strictly speaking where greater radiation fluctuations from the rod are produced, it is desirable to introduce a correcting factor varying inversely with changes in the rod radiation. For most precise results this is desirable and is included in a specific aspect of the present invention although in a broader aspect the simpler instrument referred to above is included.

Essentially in the present instrument the rod is imaged by suitable optics on different portions of a differential detector system. This may involve two detectors or a single differential detector the latter presenting many practical advantages. What is, however, vitally necessary is that there be an extremely sharp, narrow dividing line so. that in its normal position the image of the rod straddles the dividing line to produce a zero output signal and that any departure in either direction is immediately sensed resulting in an output signal of the proper polarity.

The second requirement for a proportional error signal is effected in the present invention by arranging the area of the two halves of the diiferential detector so that the areas increase evenly from a very small figure at the dividing line to a large figure at the extremes. This is effected by a mask which is preferably associated with the detector itself by being actually on the surface of a differential detector, for example of the semiconductor type. The mask may, however, be located at another point where the nature of the beam is suitable in the optical system. For this reason the term differential detector system will be used in the specification and claims to denote a system involving ditferential detectors and the other recited elements regardless of whether they are combined in a single package or form separate elements of a system. As far as the present invention is concerned it is a matter of complete indifference how the elements are arranged so long as they perform their function. From a structural and economic standpoint, however, application of the mask on or immediately adjacent to a fiat diiferential detector of the semiconductor type presents many advantages and is preferred.

The mask may take a number of shapes so long as the requirement of increasing area of active detector with increasing departure from the normal loop position of the rod is achieved. A simple illustration is a mask with two triangular areas having their apices meeting or nearly meeting at the narrow dividing line. Because of its resemblance to a stylized bow tie such a detector is referred to loosely as a bow tie detector or detector system.

It should be noted that it is not a new concept to design single detectors with effective areas which vary. The present invention, however, cannot use any and all variable area detectors. It is essential that the minimum area of each detector must approach the narrow dividing line otherwise the functions of the present invention are not achieved.

Automatic control of the loop which will constantly tend to restore it to its normal position is eflected by servo mechanisms actuated by the output signal from the differential detector system. The servo mechanisms used are conventional in form and so are indicated only diagrammatically in the more detailed description of the invention in connection with the drawings. However, a more specific aspect of the invention which includes automatic temperature, size and emissivity compensation or rather automatic compensation for different radiation intensities does involve an organization of servo mechaisms which has not been used for this purpose and so may be considered as part of this aspect of the invention. Even in the case of the automatic temperature compensation, however, electronic circuits of ordinary design are used and are, therefore, indicated diagrammatically although their organization produces a new type of servo drive for extruding rolls. I

The invention will be described in greater detail in conjunction with the drawings in which:

FIG. 1 is an elevation of a typical loop;

FIG. 2 is an optical diagram for three positions of the loop;

FIG. 3 is a diagram of the differential detector system;

FIG. 4 shows three positions of :the loop with respect to the bow tie configuration of the detector, and

PEG. 5 is a diagrammatic representation of a radiation compensator.

FIG. 1 illustrates a loop 1 of a rod ina typical steel rod mill. This loop is betweendrive rolls 2 and d the former being shown as controlled by a servo mechanism 17 in a manner which will be described below. When a rod is initially extruded the guide roll 4 is used to start the rod up to form a loop agm'nst gravity. Thereafter guide roll position is used to control the loop. This results in slow response because the roll is heavy. The present invention does not require the roll to perform this function.

Th permissible variations in the position of the top of the loop is shown by the doublearrow. The representation of FIG. 1 is in general diagrammatic and is not to scale. The permissible positions of the loop are, therefore, shown somewhat exaggerated in comparison with the size of the other elements in the drawing.

At right angles to the loop and aimed at its center is an optical scanner head shown diagrammatically in FIG. 2 with an objective lens 7, an aperture stop which images the rod on a differential detecting system 8 which will be described in greater detail below in connection with F165. 3 and 4. Fig. 2 shows the rod in three positions. The normal position, shaded, at A, the upper limit at B and the lower limit at C. These established limiting positions between which the image of the rod on the differential detecting system 8 moves.

FIG. 3 illustrates a difierential detector, for example, a lead sulfide detector which has two halves 9 and 10 separated by a narrow line 12. In the type of differential detector shown in FIG. 3 the lead sulfide is continuous with the line '12 constituted by a central electrode. The two end electrodes 11 complete the detector itself. A mask 16 divides one-half of the detector 9 and the other half 10 into two triangles in the form of a bow tie meeting at the dividing line l2. The detector is biased by direct current from the batteries or power supply 3 as usual. A rheostat 14 is provided for initial carlibration when the rod is positioned in the normal position A and a meter 15 is made to show zero output. The output is also led to two loads 18 which connect to the servo system 17 of FIG. 1.

FIG. 4 illustrates diagrammatically the location of the image of the rod, shown in dashed lines, for the positions A, B and C of FIG. 2. It will beseen that in position A it straddles the dividing line where the two triangle spices of the bow tie meet. In position B it is well up near the base of the upper triangle 9 and in position C near the base of the lower triangle- In operation when the rod is in position A where it normally is supposed to be there will be zero output from the diiferential detecting system and so the servo mechanism 17 will produce no roll speed changes. If new the rod in the loop rises the image begins to move up on the upper triangle 9 of thebow tie and an increasing output of one polarity re-.

sults. Because of the configuration of the bow tie this output is very small near the position that the loop is supposed to occupy ordinarily and becomes greater and greater as the loop movestoward either extreme. The

signal into the leads 13 changes correspondingly, the

polarity varying depending on whether the image has moved onto the upper triangle 9 of the bow tie as shownv i at B in FIG. 4 or on the lower triangle 1%) as shown in C at FIG. 4. The servo is actuated and in the first instance it speeds up rolls 2 and in the second instance slows them down. As the point of normal position is reached'the signal actuating the servo becomes less and less and the change in roll speeds decreases so that at point of balance no hunting results. This is an essential feature ,of the present invention and is effected by the geometrical shape of the bow tie detector system. Needless to say the two areas of the bow tie do not haveto be bounded by straight lines. Any other geometrical shape which brings an apex of one to an apex of the other is useful. The

straight triangular configuration is easiest to construct and as it operates with precision it is normally not necessary tor system will be twice as great and as the rod moves.

the signal actuating the servo is at all times twice as great as it would have been. This can result in undesirably large speed correction signals from the servo mechanism which could defeat the antihunting feature of the bow tie configuration. Conversely if the emissivity dropped to half the radiation falling on the detector is also halved and there may be so little energy in the output signal near the point of detector balance that response of the servo is sluggish. This is also undesirable for one of the advantages of the present invention is that correction for errors in loop position occur immediately, much faster than the reflexes of a human being observing the loop as has been done in the past. FIG. 5 illustrates how the above radiation variatio can be offset. There is shown a separate ordinary D.-C.

radiometer with an objective lens 20, and detector 21.

The detector, which is separate from the position sensing detector 8, is a simple detector the response of which varies only with the radiance of the rod and not its position and so changes with temperature, emissivity or the like. A variable gain amplifier 19 is connected between the loads 18 and the servo mechanism 17. The gain of this amplifier is controlled by the output signal from the detector 21. When this signal increases as a result of greater radiation the gainof the amplifier 19 is reduced 5 and vice versa so that the relative power applied to the servo mechanisms for different image positions on the bow tie remains unchanged with radiation changes.

It will be seen that the present invention constitutes essentially an optical instrument with associated electronically actuated controls. For steel rods the radiation is best in the infrared and so an infrared filter may be used to avoid spurious effects from general illumination. No such filter is shown as this is a conventional means for adapting the. detector system to the particular wavelength of radiation desired.

We claim: I

1. An instrument for the automatic maintenance ofa' loop of predetermined orientation in the fabrication of a continuous length of self-luminous flexible material comprising in combination,

(a) at least two sets of drive rolls between which the loop is to be maintained, means for driving said rolls,

(b) servo means for varying the rotational speed of at least one pair of rolls in each set,

(0) a differential radiation detecting system having two sections capable of transforming radiations into electrical output signals, said system being located adjacent to the loop and having a narrow dividing line between the two sections thereof, means for imaging the rod in the loop at a predetermined central position onto the dividing line,

(d) masking means in the differential detecting system providing minimum area at the dividing line and increasing in each half of the differential detector system as the image of the loop moves from the dividing line and means for actuating the servo mechanism by the output signal of the differential detector system to operate the servo mechanism in a direction to restore the loop to its predetermined position.

2. An instrument according to claim 1 in which the mask exposes a detector area in the form of a bow tie with the apices of the two triangles forming the bow tie at the dividing line.

3. An instrument according to claim 2 in which the differential detector system comprises a semiconductor detector, a central electrode constituting the narrow dividing line and two end electrodes, the mask being in close proximity to the detector layer whereby the exposed detector area is in the form of a bow tie.

4. An instrument according to claim 1 comprising a radiometer including a detector transforming radiation into electrical signals said radiometer imaging a point on the rod in the loop uniformly on the detector whereby the detector out-put is a function of radiation intensity, and variable gain amplifying means for amplifying the differential detector output and applying the applied output to the servo mechanism said amplifying means having their gain control actuated inversely by the radiometer detector output.

5. An instrument according to claim 2 comprising a radiometer including a detector transforming radiation,

into electrical signals said radiometer imaging a point on the rod in the loop uniformly on the detector whereby the detector output is a function of radiation intensity, and variable gain amplifying means for amplifying the differential detector output and applying the applied output to the servo mechanism said amplifying means having their gain control actuated inversely by the radiometer detector output.

6. An instrument according to claim 3 comprising a radiometer including a detector transforming radiation into electrical signals said radiometer imaging a point on the rod in the loop uniformly on the detector whereby the detector output is a function of radiation intensity, and variable gain amplifying means for amplifying the differential detector output and applying the applied output to the servo mechanism said amplifying means having their gain control actuated inversely by the radiometer detector output.

References Cited in the file of this patent UNITED STATES PATENTS 2,379,132 Cook June 26, 1945 2,424,193 Rost July 15, 1947 2,454,841 Sackville NOV. 30, 1948 2,877,397 Poschner Mar. 10, 1959 2,879,405 Pankove Mar. 24, 1959 2,907,565 Sauter Oct. 6, 1959 2,968,727 Otis Jan. 17, 1961 3,038,079 Mueller June 5, 1962 

1. AN INSTRUMENT FOR THE AUTOMATIC MAINTENANCE OF A LOOP OF PREDETERMINED ORIENTATION IN THE FABRICATION OF A CONTINUOUS LENGTH OF SELF-LUMINOUS FLEXIBLE MATERIAL COMPRISING IN COMBINATION, (A) AT LEAST TWO SETS OF DRIVE ROLLS BETWEEN WHICH THE LOOP IS TO BE MAINTAINED, MEANS FOR DRIVING SAID ROLLS, (B) SERVO MEANS FOR VARYIGN THE ROTATIONAL SPEED OF AT LEAST ONE PAIR OF ROLLS IN EACH SET, (C) A DIFFERENTIAL RADIATION DETECTING SYSTEM HAVING TWO SECTIONS CAPABLE OF TRANSFORMING RADIATIONS INTO ELECTRICAL OUTPUT SIGNALS, SAID SYSTEM BEING LOCATED ADJACENT TO THE LOOP AND HAVING A NARROW DIVIDING LINE BETWEEN THE TWO SECTIONS THEREOF, MEANS FOR IMAGING THE ROD IN THE LOOP AT A PREDETERMINED CENTRAL POSITION ONTO THE DIVIDING LINE, (D) MASKING MEANS IN THE DIFFERENTIAL DETECTING SYSTEM PROVIDING MINIMUM AREA AT THE DIVIDING LINE AND INCREASING IN EACH HALF OF THE DIFFERENTIAL DETECTOR SYSTEM AS THE IMAGE OF THE LOOP MOVES FROM THE DIVIDING LINE AND MEANS FOR ACTUATING THE SERVO MECHANISM BY THE OUTPUT SIGNAL OF THE DIFFERENTIAL DETECTOR SYSTEM TO OPERATE THE SERVO MECHANISM IN A DIRECTION TO RESTORE THE LOOP TO ITS PREDETERMINED POSITION. 